Respiratory tract deposition of particles at a busy street

Traffic is one of the major sources of urban air pollution. To relate exposure to adverse health effects it is important to determine the deposition probability of the inhaled particles in the human respiratory tract. The aims of this study were to: 1) experimentally determine the respiratory tract deposition of a typical urban street aerosol for a group of healthy adults, 2) measure the hygroscopic properties of the particles, and 3) provide a tool/model to estimate particle deposition in other similar environments. The size dependent deposition of 12-580 nm particles was determined in 9 healthy subjects breathing by mouth on the windward side of a busy street (6 lanes, 65 000 vehicles/day) in Copenhagen, Denmark. Measurements were carried out with a recently developed set-up, RESPI (Londahl et al. 2006), that was extended with a novel processing unit to account for particle size changes in the lungs (Londahl et al. 2009). In RESPI particle concentrations in inhaled and exhaled air is measured with a scanning mobility particle sizer (SMPS). The aerosol was characterized both at the curbside and, to obtain the background concentration, at rooftop level. Particle hygroscopicity, a key parameter affecting respiratory tract deposition, was also measured with a hygroscopic tandem differential analyser (HTDMA) at the same time of exposure. The modelled deposition fraction was determined by adjusting the well-established ICRP model for the measured hygroscopic growth factors. The size dependent deposition fractions of the particles in the range 12-580 nm is shown in Figure 1.

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